In the manufacture of micromechanical sensors having diaphragm structures of greatly varying functionality, the use of sawing to separate the chips of finished processed components represents a process known per se. For diaphragm manufacturing, in particular for microphones and pressure sensors, a cavity volume may be created on the rear side. In the case of closed diaphragms having a sealing function from the front side to the rear side and also a comparatively high mechanical stability, a conventional wafer sawing process may be applied without a particularly high risk of diaphragm damage. In the case of closed diaphragms, there is also not a high risk of irreversible sticking of the diaphragm to layers lying underneath when sawing from the wafer front side, as a result of the liquid media used during sawing for removing sawing slurry.
However, the conditions are different in the case of structured diaphragms. These diaphragms are no longer completely closed, since they are perforated, for example. Such structured diaphragms may be used, for example, for stress decoupling, since independence of the sensitivity from intrinsic layer stress parameters may be achieved via the design through suitable diaphragm geometries. Such design-related measures play, inter alia, a large role for the manufacturing of microphones at high reproducibility and yield, in order to achieve independence from layer parameters which are difficult to control, such as the intrinsic stress. However, the sealing function with respect to the wafer rear side is eliminated in such diaphragms, which complicates sawing using liquid media and entails a high risk for the component as a result of the penetration of liquid and contaminants into the capacitive pickup structure.
So-called “stealth dicing,” also known as “Mahoh dicing,” represents an alternative to classic wafer sawing for chip separation. The wafer material is amorphized using a laser beam, whereby mechanical stresses are induced in the wafer. The thus produced target breakpoints cause the separation of the chips upon expansion of the wafer on a film. In this method, there is effectively no excess material, so that it is no longer necessary to use liquid media to remove this material during the separation process. However, this method has the disadvantage that depending on the wafer thickness, multiple or even numerous laser scans are required. The wafer throughput thus drops and the costs of the method rise.
German patent document DE 197 30 028 C2 discusses a method for using an excimer laser to separate and process semiconductor chips precisely at the edges, the chips being produced in a group on a semiconductor substrate and made of AIII-BV compound semiconductors. The excimer laser operates in the range of ≦100 fs pulse duration and ≦250 nm wavelength. In the method, an initial cut, which is shorter than the total length of the separation line, is produced on a substrate edge by displacing the incidence area of the laser beam. The initial cut is oriented in the separation line direction of a substrate surface to be processed along the desired separation line, which is located in a cleavage plane corresponding to a crystallization direction of the semiconductor substrate. The initial cut is produced as a notch in such a way that it results in an independent cleavage procedure and thus the separation of the semiconductor chip in the separation line direction. It is disadvantageous therein that high power densities between 5×1013 and 2×1014 W/cm2 are required to produce the initial cut according to the description.